Method for managing the heating of fluids flowing through a network of submarine pipelines

Abstract

A method of managing the heating of fluids flowing in an undersea pipe network (2-1) providing a connection between a surface installation (6) and at least one undersea production well (4). The method releasably connecting at least one fluid heater station (14a, 14b) to an undersea pipe and controlling the heater station as a function of the mode of operation of the pipe network.

The invention claimed is: 
     
       1. A method of managing the heating of fluids flowing in an undersea pipe network providing a connection between a surface installation and at least one undersea production well, wherein the undersea pipe network comprises two main pipes connected together at the sea bottom and each connected to the surface installation so as to form at least one fluid circulation loop; a plurality of secondary pipes connecting production wells to the two secondary pipes; and two connection pipes connecting together the two main pipes downstream from the fluid heater stations, the method comprises:
 releasably connecting at least one fluid heater station to an undersea pipe by a bypass pipe connected to the undersea pipe, to selectively direct the fluids flowing in the undersea pipe through the bypass pipe and towards the fluid heater station for heating the so-directed fluids, and for returning the so-heated fluids to the undersea pipe, and controlling the operation of said fluid heater station as a function of a mode of operation of the pipe network; 
 connecting each main pipe to at least one fluid heater station downstream from the secondary pipes, and activating the fluid heater stations in a stage of normal operation of the pipe network to maintain the fluids at all points of the network at a temperature higher than a predetermined temperature threshold; and 
 in a preservation stage of the undersea pipe network:
 closing the secondary pipes and the main pipes between the two connection pipes while opening the connection pipes, and activating the heater stations to maintain the fluids at all points in an upstream fluid circulation loop at a temperature higher than a predetermined temperature threshold; and 
 injecting a processed fluid into the main pipes of a downstream fluid circulation loop to purge the fluids it contains. 
 
 
     
     
       2. The method according to  claim 1 , wherein, in a stage of restarting the pipe network following a preservation stage, the method comprises reactivating the fluid heater stations while keeping closed the secondary pipes so as to heat the main pipes, and subsequently reopening the secondary pipes progressively in order to restart production. 
     
     
       3. The method according to  claim 1 , wherein, in a stage of restarting the undersea pipe network following a preservation stage, the method comprises:
 stopping injection of a processed fluid into the main pipes of the downstream fluid circulation loop; 
 reopening the main pipes between the connection pipes; 
 closing the two connection pipes so as to merge together the upstream and downstream fluid circulation loops; 
 injecting methanol into at least one of the connection pipes in order to prevent hydrates forming therein; and 
 reopening the secondary pipes progressively in order to restart production. 
 
     
     
       4. The method according to  claim 1 , wherein, in a stage of preserving the undersea pipe network, the method comprises stopping the fluid heater stations and depressurizing the upstream fluid circulation loop in order to avoid hydrates forming in the upstream loop. 
     
     
       5. The method according to  claim 1 , wherein the undersea pipe network comprises:
 a production pipe connected to the surface installation; 
 a plurality of secondary pipes connecting production wells to the production pipe; and 
 a service pipe connected to the production pipe downstream from the secondary pipes; 
 the method further comprising connecting the production pipe to at least one fluid heater station downstream from a connection with the service pipe, and activating the fluid heater station in a stage of normal operation of the pipe network in order to maintain the fluids at all points in the network at a temperature higher than a predetermined temperature threshold. 
 
     
     
       6. The method according to  claim 1 , wherein at least one of the undersea pipes is connected to at least two fluid heater stations installed in series or in parallel.